Dental unit waterlines: source of contamination and cross ... - CCIH

104 S. Kumar et al.
unrecognised or unreported because of the failure
to associate exposure to DUW or aerosols with the
development of specific infections. Sporadic infections
such as Pontiac fever, also caused by Legionella
spp., are less likely to be investigated or
notified to health authorities (www.bda.org). 61
Risk factors identified in domestic acquisition of
Legionnaires’ disease are of relevance in preventing
infection in the dental surgery. Multivariate
analysis showed an increased risk of infection
following recent plumbing repairs, the use of an
electric rather than a gas water heater, smoking,
and working >40 h per week. 61
Approaches to risk reduction
DUW cleaning and disinfection systems
DUW treatment agents can be introduced into
DUWs from independent reservoir bottles or from
disinfectant delivery devices connected to the DCU
water supply inlet. In the case of DCUs connected to
a municipal water mains supply, it is imperative
that the connection is turned off prior to DUW
treatment to prevent contamination of mains water
with treatment agent. After treatment, DUWs
should be flushed thoroughly using clean water
before DCUs are used for patient treatments.
DCU manufacturers have developed a new generation
of DCUs with integrated DUW cleaning
systems that facilitate and simplify DUW disinfection.
Indeed other DCU manufacturers are likely to
follow suit, as the dental community becomes
more aware of the problem of DUW contamination.
12,13 WCSä (Water Cleaning System) was
found to be very effective at eradicating DUW biofilm
in these DCUs when used with Sanosilä (a
highly effective, universally applicable disinfectant
having two main components: hydrogen peroxide
and silver) and consistently provided
output water with bacterial densities below the
ADA recommended threshold of w200 cfu/mL for
up to seven days post disinfection. The microprocessor-controlled
WCS was originally developed
to be retrofitted to existing Planmecaä DCUs having
a mains water supply. Some DUWs contain a microprocessor-controlled
system where waterlines
are filled with disinfectant and subsequently automatically
flushed with clean water during the disinfection
cycle. If the cycle is not completed
properly or a power failure occurs during the cycle,
an error message is displayed on the DCU instrument
console. 13,62 While this error message is
displayed, all DCU functions are locked, preventing
the DCU from being used. The WCS is semi-
automated and requires the operator to fill the
disinfectant container with disinfectant, to turn
off a valve on the mains water supply and to place
DCU instrument hoses into special receivers. DUW
cleaning is activated from a keypad on the DCU
control console and disinfectant is automatically
fed into each DUW. Following this the DCU electrical
supply is switched off to allow the disinfectant
in situ to take effect. When the electrical power is
turned back on, a code message on the DCU control
console display prompts the operator to flush
the DUWs. This is initiated by disconnecting the
disinfectant container module and turning on the
mains water supply switch. The longer-term
goal should be for fully automated disinfection systems
that are validatable. Recently Planmeca
developed a more advanced microprocessor-controlled
DUW cleaning system called the Water Management
System (WMS), a fully integrated and
automated DUW cleaning system that requires
minimal effort on the part of the operator. The
WMS is more advanced and automated than the
WCS and also contains many additional features,
including an air gap.
Anti-retraction valves and retrograde
aspiration of oral fluids
The implicated source of contamination was reaspiration
of fluid from the oral cavity that
occurs when negative pressure is generated on
stopping equipment. Recently, molecular techniques
were employed to demonstrate the recovery
of viral particles and human DNA in
waterlines servicing the air turbine and prophy
angle handpiece. 63 Anti-retraction valves (also
known as check valves) will limit re-aspiration
and are most efficacious when fitted immediately
distal to the handpiece. As with any component
of the water supply line they are subject to clogging
due to biofilm deposition and fatigue. In order
to ensure adequate mechanical functioning,
they require regular maintenance and programmed
replacement. Autoclaving of handpieces
after use and flushing of units for 30 s at the end
of patient treatment and for 2.5 min at the end
of the day will augment the action of the anti-retraction
valve and should help to eliminate any
aspirated fluid. 64 Some manufacturers have incorporated
anti-retraction valves within the handpiece
design, permitting autoclaving of the
valve between patients. Backflow from dental
units to the mains water supply may occur and
it may be necessary to install check-valves to
prevent this occurring. 65